The present invention relates, in general, to an electromotive drive for a furniture item, and more particularly to a lifting device for elevating and lowering a furniture item.
Electromotive drives for furniture items are known in a wide variety of designs for positionally adjusting furniture components, and typically include a drive motor, a reduction gear unit and a rotatably driven spindle which supports a spindle nut secured against carrying out a rotation movement and carrying a lifting tube which is arranged inside an outer flanged tube and moveable in and out relative thereto. For safety reasons, the drive motors are DC motors which are supplied with a safety voltage. The reduction gear unit is normally a worm gearing as the speed ratio of the rotor of the drive motor must be very high compared to the speed of the spindle. Therefore, the linearly moving spindle nut travels at an extremely low velocity. Normally, a connection piece in the form of a fork head is securely mounted to the free end of the lifting tube.
Heretofore, furniture drives are generally only required to apply a force that is capable to overcome the own weight of the furniture item; However, there is increasingly a demand for drives which are capable to adjust the height of furniture items that are exposed to a load, for example, tops of working tables or like articles having objects placed on them. Moreover, it is also desirous to increase the adjusting speed of such furniture items.
It is thus an object of the present invention to provide an improved electromotive drive for furniture items, obviating the afore-stated drawbacks.
In particular, it is an object of the present invention to provide an improved electromotive drive for furniture items by which the thrust force generated by the driving power of the drive motor can be supplemented or the driving power of the motor can be reduced while still generating a same thrust force.
These objects, and others which will become apparent hereinafter, are attained in accordance with the present invention by providing a drive motor mounted to a housing and interacting with a reduction gear unit, a rotating spindle driven by the drive motor via the reduction gear unit and carrying a spindle nut which is secured against executing a rotation movement so as to move in a linear direction, a flanged tube mounted to the housing, a lifting tube received in the flanged tube and mounted to the spindle nut so as to be movable between retracted and extended positions when the spindle rotates and the nut is moved in a linear direction, and at least one gas spring arranged within the flanged tube for assisting the lifting tube during a movement of the lifting tube to the extended position, wherein the gas spring has a piston rod which reciprocates in synchronism with the lifting tube.
Structure and operation of a gas spring are generally known to a person skilled in the art. Although their reliability has been shown for use in many applications, gas springs are incapable to tilt or lift an attached furniture component when relatively great forces are required. Through the novel and inventive combination of an electric motor with a gas spring, the thrust force produced by the electric motor can now be increased by the force applied by the gas spring so that greater loads can be moved than would have been feasible with conventional furniture drives. The gas spring is, however, not only employed to increase the thrust force, but in fact serves a dual function, because in addition to the increase of the thrust force for lifting or upward tilting of the furniture item, the gas spring operates also as a brake when the furniture item descends. This is important because the own weight of the furniture item normally results in an accelerated descent. There is also the added advantage that the braking force is applied with the aid of the gas spring. A reliable operation is realized when the forces applied by the spindle nut and the gas spring act in a same direction as the spindle nut. The drive can be so dimensioned as to apply only the force that, upon retraction of the spindle nut, is necessary to implement a retraction of the piston rod of the gas spring.
According to another feature of the present invention, the spindle is a hollow spindle for accommodation of the gas spring, thereby realizing a simple and compact configuration. As the spindle turns when the drive motor operates, the bore of the hollow spindle may be so sized as to enclose the gas spring without encountering friction forces that may adversely affect the power of the drive. Thus, the drive can be so configured that no fastening members for the gas spring become necessary as the spring can be supported by the housing or connection parts. This compact construction permits the provision of only a single gas spring for the furniture drive, whereby the length is only slightly smaller than the length of the spindle. When desiring to further increase the forces for lifting the furniture items, it may be suitable to utilize more than one gas spring, whereby the gas springs are positioned outside of the spindle and within the flanged tube at a same angular relationship. In this case, the forces applied by the individual gas springs add up.
In the event the electromotive furniture drive includes one or more gas springs, positioned outside the spindle, it is suitable to configure the lifting tube as multi-chamber tube with a plurality of chambers defining central longitudinal axes in spaced-apart parallel relationship to one another and to a central longitudinal axis of the spindle, whereby one of the chambers receives the spindle and the other chamber or chambers receive the gas spring or gas springs. Although this configuration does not impact on the applied force and the velocity of the lifting tube, the overall look is improved as the gas spring or gas springs become invisible.
According to another feature of the present invention, the lifting tube may have a cross section substantially in the form of an 8, when the gas spring is arranged outside the spindle. Suitably, the flanged tube may then exhibit a kidney-shaped cross section whereby the constriction on one side is located in the area between the two chambers of the lifting tube. In the event that only the spindle is positioned within a chamber whereas the gas spring is disposed in a free interior space between the inside wall surface of the lifting tube and the spindle, the flanged tube may exhibit an oval-shaped cross section. A material-saving construction is realized by profiling the inside wall surface of the flanged tube in circumferential direction, for example through provision of webs and recesses extending in longitudinal direction of the flanged tube.
According to another feature of the present invention, the piston rods of the gas springs move in and out with respect to a motor-distal end of the flanged tube and are coupled with one another and with the lifting tube. In this manner, the movements of the piston rods of the gas springs and the lifting tube are synchronized, whereby the interconnection with the lifting tube results in a transfer of the full force. Suitably, when the flanged tube accommodates two gas springs, which are offset to one another at an angle of 180xc2x0, a pin can be used to couple the piston rods and the lifting tube to one another.
According to yet another feature of the present invention, the gas springs may be coupled at their motor-proximal side with the flanged tube by means of a bolted connection.
According to another aspect of the present invention, the gas spring or gas springs may be controllable so that the furniture item may be stopped in any position. The control is preferably implemented by a valve. Through controlling the gas stream, a brake action is produced so that, optionally, the velocity of the output elements of the furniture drive can be regulated.
According to still another aspect of the present invention, the furniture drive is provided with a release mechanism, so that the descent of the attached furniture item can be implemented at a higher speed. The release mechanism includes a first coupling disk secured in fixed rotative engagement on the output journal of the drive, a second coupling disk wedged on the spindle at the end proximate to the first coupling disk and secured against execution of a rotation movement, and a coupling sleeve movable in an axial direction to realize an engagement of the first and second coupling disks, whereby the first coupling disk and the coupling sleeve have complementary engagement surfaces such that a movement of the lifting tube to the upwardly directed position is accompanied by a synchronous movement of the coupling sleeve through engagement by the first coupling disk. When implementing the adjustment in the same direction by hand, the coupling sleeve turns whereas the first coupling disk is at a standstill. The manual operation can be initiated in a simple manner by mounting to the coupling sleeve a release element which is shiftable in axial direction relative to the second coupling disk, and by providing compression springs for loading the coupling sleeve into engagement with the first coupling disk.
Through interaction of the coupling sleeve with both coupling disks, the upward and downward adjusting movements of the furniture item can be realized at running drive during normal operation. As, however, the coupling sleeve can travel in axial direction, there is the option to disengage the meshing engagement surfaces during normal operation so that the downwardly directed movement of the attached furniture item can be executed in a short time at respectively greater speed. When it is desired to lift the furniture item by hand, the drive runs in reverse as a movement of an articulated lever, provided to convert a linear movement of the drive in a tilting of the furniture item being adjusted, or vice versa, conjointly moves the spindle nut. The adjusting spindle is not self-locking and thus is caused to turn as the spindle nut moves linearly, resulting in a rotation of the second coupling disk and the attached coupling sleeve. By suitably shaping the engagement surfaces, it is possible to realize that the coupling sleeve rotates relative to the stationary first coupling disk. This is possible, because the coupling sleeve can shift in axial direction.
The release element may be a claw, a pull element, for example a Bowden cable or similar mechanism. The axial displacement of the release element relative to the second coupling disk may be realized, for example, by a suitably dimensioned keyway connection or a splined connection. When the release element is not in use, the compression springs urge the profiled engagement surfaces into meshing engagement. During lifting of the furniture item by hand, the compression springs permit the axial displacement required to rotate the coupling sleeve.
The release mechanism may also be implemented by rotatably mounting the worm wheel of the drive on a guide member which is securely fixed to the spindle. A coupling wheel is secured in fixed rotative engagement on the guide member but movable in axial direction for engagement and disengagement with the worm wheel. In this construction, the worm wheel is so designed that the power train to the adjusting spindle from the worm wheel during normal operation is transmitted via the coupling wheel and the guide member. When it is desired to execute the downward movement in a shortest possible time through a respective greater lowering speed, the coupling wheel is disengaged from the worm wheel. The spindle, the guide member and the coupling wheel then turn while the worm wheel and the drive are at a standstill. This configuration only insignificantly, if at all, alters the dimensions of the furniture drive compared to drives without release mechanism. Linkage of the worm wheel with the coupling wheel is realized by providing the worm wheel with circular teeth for meshing with complementary teeth on a confronting side of the coupling wheel. This results in a slip-free connection that can be subjected to great stress. Suitably, the teeth have a serrated configuration, and each tooth is bounded with respect to the rotation axes by a steep flank and a flat flank. During normal operation, the torque is transmitted via the steeper flanks of the teeth of the worm wheel and the coupling wheel when the furniture item is moved up. This torque transmission is executed, however, only in the respective rotation direction. In the opposite rotation direction, for example when lowering the attached furniture item, the coupling wheel turns and disengages form the worm wheel and shifts in axial direction.